At present, the sealing requirement of regulating valves chosen by most of thermal power plants and petrochemical companies to the closure of the valves is not high, i.e., allows a small leakage of the valves. However, for a regulating valve that is required to be in a working condition of tight closure, the valve manufacturers at home and abroad have not found effective measures and methods to protect and prevent a sealing surface from being damaged, both of which are to directly use the outer side of the lower end surface of a valve core and an inclined surface of a valve seat as sealing surfaces. FIG. 5 is a sealing structure of an existing regulating valve. In the valve adjustment process, a medium continuously erodes the sealing surface at the end part of the valve core via throttle holes of a valve sleeve to produce non-uniform erosion to the sealing surface at the end part of the valve core. When the valve is closed, there is a gap between the eroded portion of the sealing surface of the valve core and the sealing surface of the valve seat.
The existing regulating valve hereby has the following defects: (1) when the valve regulates the medium, the front end of the valve core takes the effects of changing a throttling area and regulating medium parameters; the sealing surface at the front end of the valve core always suffers from a severe impact from the high-speed throttling medium, and therefore the sealing surface of the valve core will be damaged by erosion after being used for a long time; however, the erosion damage of the sealing surface is non-uniform, and therefore, the valve is closed, a gap will be formed between the eroded portion and the original sealing surface of the valve seat, resulting in internal leakage. (2) Due to internal leakage and large pressure difference at this time, the valve core and the sealing surface of the valve seat will be severely damaged by erosion at the same time, and from then on the valve cannot be sealed. (3) As a throttling regulation portion is damaged, the valve cannot be regulated properly, thereby affecting the normal operation of the system. (4) As a leakage occurs to the valve in a very short period of time, and with the use time increases, the leakage amount also increases. This situation has been continued for a minor repair time of the crew, in order to treat the valve, which will bring great economic losses to users (loss of high temperature and high pressure medium, and increase of fed water to a boiler), and therefore, the losses will far exceed the own value of the valve. (5) Since the structure of the chosen valve is not suitable for such conditions, even if new spare parts are replaced, it is also impossible to completely avoid such a thing; and the valve will be subject to great damage, which will increase the repair amount of the valve, the workload for the replacement of the valve and spare parts and other costs.